* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download I. Introduction
Vectors in gene therapy wikipedia , lookup
Oncogenomics wikipedia , lookup
Segmental Duplication on the Human Y Chromosome wikipedia , lookup
Epigenetics of diabetes Type 2 wikipedia , lookup
Gene desert wikipedia , lookup
Epigenetics of neurodegenerative diseases wikipedia , lookup
Genetic engineering wikipedia , lookup
Essential gene wikipedia , lookup
Polymorphism (biology) wikipedia , lookup
Long non-coding RNA wikipedia , lookup
Therapeutic gene modulation wikipedia , lookup
Pathogenomics wikipedia , lookup
Human genome wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Nutriepigenomics wikipedia , lookup
Public health genomics wikipedia , lookup
History of genetic engineering wikipedia , lookup
Ridge (biology) wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Genome evolution wikipedia , lookup
Minimal genome wikipedia , lookup
Skewed X-inactivation wikipedia , lookup
Dominance (genetics) wikipedia , lookup
Quantitative trait locus wikipedia , lookup
Gene expression programming wikipedia , lookup
Gene expression profiling wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Neocentromere wikipedia , lookup
Genomic imprinting wikipedia , lookup
Y chromosome wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Designer baby wikipedia , lookup
Microevolution wikipedia , lookup
Shier, Butler, and Lewis: Hole’s Human Anatomy and Physiology, 13th ed. Chapter 24: Genetics and Genomics Chapter 24: Genetics and Genomics I. Introduction A. Genetics is the study of inheritance of characteristics. B. Genes are sequences of nucleotides of the nucleic acid DNA. C. Genes are part of structures called chromosomes. D. A gene’s nucleotide sequence tells a cell how to link a certain sequence of amino acids together to construct a specific protein molecule. E. A genome is the complete set of genetic instructions in a human cell. F. Somatic cells have two sets of chromosomes. G. Diploid means having two sets of chromosomes or 46 chromosomes in humans. H. Sex cells have one set of chromosomes. I. Haploid means having one set of chromosomes or 23 chromosomes. J. The human genome includes 20,325 protein-encoding genes, constituting the exome. K. The exome accounts for only a little less than 2% of the 3.2 billion DNA bases of the human genome. L. Genomics is the study of the human body in terms of multiple, interacting genes. M. Proteonomics focuses on the spectrum of proteins that specific cell types produce. N. Environmental factors that affect how genes are expressed are chemical, physical, social, and biological. II. Modes of Inheritance A. Introduction 1. The probability that a certain trait will occur in the offspring of two individuals can be determined by knowing how genes are distributed in meiosis and the combinations in which they can come together at fertilization. 2. The patterns in which genes are transmitted in families are termed modes of inheritance. 3. Gregor Mendel deciphered the modes of inheritance in the 1860’s by breeding pea plants. B. Chromosomes and Genes Come in Pairs 1. Karyotypes are chromosome charts that display the 23 chromosome pairs in size order. 2. Autosomes are chromosome pairs 1 through 22 and do not carry genes that determine sex. 3. Sex chromosomes are chromosome pair 23 and determine sex. 4. Most chromosomes contain hundreds or thousands of genes. 5. Alleles are variant forms of genes that differ in DNA sequence. 6. Homozygous alleles are identical. 7. Heterozygous alleles are different. 8. Genotype is the particular combination of genes in a person’s genome. 9. Phenotype is the appearance or health condition of the individual that develops as a result of the ways the genes are expressed. 10. A wild type allele is associated with the most common or normal phenotype. 11. A mutant allele is a change from the wild type. C. Dominant and Recessive Inheritance 1. A dominant allele is one that masks that of another allele. 2. A recessive allele is one that is masked by a dominant allele. 3. An autosomal gene is located on a nonsex chromosome. 4. An X-linked gene is located on an X chromosome. 5. A Y-linked gene is located on a Y chromosome. 6. Mode of inheritance refers to whether a trait is dominant or recessive, autosomal, or carried on a sex chromosome. 7. An autosomal condition is equally likely to affect either sex. 8. X-linked characteristics affect males much more than females. 9. Recessive conditions can skip a generation because a person most likely inherits a recessive condition from two healthy parents who are each heterozygotes. 10. Dominant conditions do not skip generations because a person who inherits the condition has at least one affected parent. 11. The disease cystic fibrosis is an example of an autosomal recessive disorder. 12. If both parents are heterozygotes for the trait that causes cystic fibrosis, there is a 25% chance that their offspring will be homozygous dominant, a 50% chance their offspring will be heterozygous, and a 25% chance their offspring will be homozygous recessive. 13. A Punnett square is a table used to predict the probabilities of particular genotypes occurring in offspring. 14. A pedigree is a diagram that depicts family relationships and genotypes and phenotypes when they are known. 15. An example of an autosomal dominant disorder is Huntington disease. 16. Most of the 3,000 or so known human inherited disorders are autosomal recessive. D. Different Dominance Relationships 1. Incomplete dominance is a type of inheritance in which the heterozygous phenotype is intermediate between that of either homozygote. 2. An example of a trait inherited through incomplete dominance is familial hypercholesterolemia. 3. Codominant means different alleles are both expressed in a heterozygote (like with type AB blood). 4. The genotypes of individuals with the following blood types are: type A – IAIA or IAi type B – IBIB or IBi type AB - IAIB type O - ii III. Factors That Affect Expression of Single Genes A. Introduction 1. The same allele combination can produce different phenotypes because of the influences of nutrition, toxins, illnesses, or the activities of other genes. 2. A major goal of genomics is to identify and understand the interactions of alleles, nutrition, environmental factors, illnesses, and activities of other genes. B. Penetrance and Expressivity 1. Completely penetrant means that everyone who inherits it has some symptoms. 2. Incompletely penetrant means some individuals with it do not express the associated phenotype. 3. A phenotype is variably expressive if the symptoms vary in intensity in different people. C. Pleiotropy 1. Pleiotropy is a single genetic disorder that can produce several symptoms. 2. An example of a disease that exhibits pleiotropy is Marfan syndrome. D. Genetic Heterogeneity 1. Genetic heterogeneity is when the same phenotype may result from the actions of different genes. 2. An example of a condition that exhibits genetic heterogeneity is hereditary deafness. IV. Multifactorial Traits A. Polygenic means the traits are determined by more than one gene. B. Variations in height are due to multiple genes. C. Variations in skin color are due to three or more genes with two alleles each. D. Variations in eye color are due to multiple genes; four have been found so far. E. Multifactorial traits are traits molded by one or more genes plus the environment. F. Examples of multifactorial traits are height, skin color, and certain illnesses. V. Matters of Sex A. Introduction 1. A human female is termed homogametic because she has two of the same type of sex chromosome. 2. A human male is termed heterogametic because his two sex chromosomes are different. B. Sex Determination 1. A male is conceived when a sperm containing a Y chromosome fertilizes an egg (which has an X chromosome). 2. A female is conceived when a sperm containing an X chromosome fertilizes an egg. 3. The gene responsible for being male is the SRY gene. 4. The gene responsible for being female is the Wnt4 gene. C. Sex Chromosomes and Their Genes 1. The X chromosome has more than 1500 genes. 2. The Y chromosome has 231 protein-encoding genes. 3. The three groups of Y-linked genes are genes at the tips of the Y chromosome that have counterparts on the X chromosome, genes that are very similar in DNA sequence to certain genes on the X chromosome and genes that are unique to the Y chromosome. 4. Y-linked genes are transmitted from father to sons. 5. Any gene on the X chromosome of a male is expressed in his phenotype because he has no second allele on a second X chromosome to mask its expression. 6. An allele on an X chromosome of a female may or may not be expressed because it depends on whether it is dominant or recessive and upon the nature of the allele on the second X chromosome. 7. The male is said to be hemizygous for X-linked traits because he has half the number of genes on the X chromosome that the female has. 8. Examples of X-linked recessive traits are red-green color blindness and hemophilia. 9. If a mother is heterozygous for a particular X-linked gene, her son has a 50% chance of inheriting either allele from her. 10. X-linked genes are passed on from mother to son. 11. A daughter can inherit an X-linked disorder only if her father is affected and her mother is a carrier. D. Gender Effects and Phenotypes 1. A sex-linked trait is one that affects a structure or function of the body that is present in only males or only females. 2. Sex-influenced inheritance is a type of inheritance in which an allele is dominant in one sex but recessive in another. 3. A heterozygous male is bald and a heterozygous female is not bald because the baldness allele is dominant in males but recessive in females. 4. Genomic imprinting is an effect in which the expression of a disorder differs depending upon which parent transmits the disease-causing gene. VI. Chromosome Disorders A. Polyploidy 1. Polyploidy is the condition of having an extra set of chromosomes. 2. Polyploidy results from formation of a diploid gamete from nondisjunction. 3. The fate of a polyploid human is death as an embryo, fetus, or rarely as a young child. B. Aneuploidy 1. Aneuploid means a condition of missing a chromosome or having an extra one. 2. Euploid means a normal chromosome number. 3. Anueploidy results from nondisjunction. 4. Nondisjunction is a meiotic error in which a chromosomal pair fails to separate, producing a sperm or egg that has two copies of a particular chromosome or none. 5. Autosomal aneuploidy often results in mental retardation. 6. Trisomy is the condition of having one extra chromosome. 7. Monosomy is the condition of missing one chromosome. 8. Translocation is a type of aberration in which one copy of a chromosome exchanges parts with a different chromosome. 9. Trisomy 21 is known as Down syndrome. 10. Other common autosomal trisomies are trisomy 13 and trisomy 18. 11. Turner syndrome results from missing one X chromosome in a girl. 12. Klinefelter syndrome results from having an extra X chromosome in a boy. 13. Jacobs syndrome results from having an extra Y chromosome in a boy. C. Prenatal Tests 1. An ultrasound can detect growth rate, head size, and size and location of organs. 2. Maternal serum markers can detect an underdeveloped fetal liver that may indicate an increased risk of trisomy. 3. Amniocentesis is a procedure in which a needle is inserted into the amniotic sac to draw amniotic fluid and it can detect chromosomal abnormalities. 4. Chorionic villus sampling is the removing of chorionic villus cells, and it can detect chromosomal abnormalities. 5. Fetal cell sorting is a process that samples only maternal blood, and it can detect genetic abnormalities of the fetus. VII. Genetics and Personalized Medicine A. People may have their entire genomes sequenced, but they might not know what to do with the information. B. Single-gene tests or symptoms may be more useful than knowing the whole genome. C. Gene expression means identifying which genes are active in particular cell types under particular conditions. D. Changes in gene expression accompany all diseases, not just the rare ones caused by mutations in a single gene. E. Analyzing gene expression for the whole exome can suggest new ways to treat diseases by identifying biochemical changes that traditional tests do not reveal. F. Pharmacogenetics tests are based on gene expression profiling that predict which drugs will be more effective and least likely to cause adverse affects in a particular patient. G. Physicians can use pharmacogenetics to select anticoagulants, antidepressants, cancer medications, and cholesterol-lowering drugs.